The UK must maintain "political goodwill" if it wants a deal on the Northern Ireland Protocol, the EU said on Monday, in a warning to Liz Truss not to repeat Lord Frost's threats to trigger Article 16 of the Brexit treaty.
The Foreign Secretary agreed to further negotiations at a meeting in Brussels with Maros Sefcovic, the European Commission vice-president, after another week of talks brought no breakthrough.
Officials were locked in negotiations over how to cut checks on British goods exported to Northern Ireland, which continues to follow some EU rules to prevent a hard land border.
"If political goodwill is maintained, our discussions could lead to a timely agreement on durable solutions that would immediately and significantly help operators on the ground," Mr Sefcovic said.
The Foreign Secretary has adopted a less confrontational approach than her predecessor Lord Frost, who threatened to unilaterally suspend parts of the protocol by using Article 16.
This enraged Brussels and led to warnings the EU could cancel the Brexit trade deal with the UK.
Brussels offered in October to cut many checks on British goods in return for bolstered market surveillance, to ensure no goods destined for Northern Ireland cross the border into Ireland, an EU member state.
Mr Sefcovic warned that negotiators had to remain "laser focused" on cutting those checks, in a sign that the EU continues to reject British demands over the role of the European Court of Justice.
Ms Truss has called for a new arbitration system to prevent the EU being able to take the UK to its top court in disputes over the implementation of European law in Northern Ireland.
"There has been progress," Ms Truss said after the meeting, before refusing to give a "running commentary" on the talks.
"We've had constructive discussions and I'm absolutely determined to protect political stability and peace in Northern Ireland," she said.
Northern Ireland will hold elections for the Stormont Assembly on May 5. Officials on both sides have fears the ballot could become a de facto referendum on the protocol if a deal is not reached in February or March.
Mr Truss has warned that the treaty has lost the consent of unionists, who fear it is driving a wedge between Northern Ireland and the rest of the UK, which argues it has a chilling effect on trade with Britain.
She was asked if protocol talks could be paused before campaigning in Northern Ireland begins in earnest.
"I want to get this done. So I'm not putting any barriers on that. We're putting as many resources as we can into making this work and making things happen for the people of Northern Ireland," she said.
A UK source added: "Both sides believe a deal can be done. There's genuine optimism and Liz has brought refreshing momentum and positivity to the talks."
But EU officials are pessimistic a deal can be struck while there are still questions hanging over Boris Johnson's future as Prime Minister.
"It's less Stormont and more the Tory party leadership," an EU source said. "I would guess that nothing would happen given that question mark is there."
Mr Sefcovic also held talks with Simon Coveney, Ireland's foreign minister, and earlier discussed ongoing UK-EU negotiations over Gibraltar with Spain's foreign minister.